1. Technical Field
The present disclosure relates to an apparatus and method for encapsulating fluid in a shock absorber, and a shock absorber manufactured thereby. More particularly, the present disclosure relates to an apparatus and method for encapsulating gas and oil in a tube of a mono-tube-type shock absorber, and a shock absorber manufactured thereby.
2. Description of the Related Art
In general, a vehicle is provided with shock absorbers between a vehicle frame and an axle to enhance driving comfort by buffering impact or vibration transmitted from the road to the axle during driving. The shock absorber is filled with gas and oil to improve damping force and is sealed.
According to the structure, the shock absorber is classified into a twin tube-type shock absorber, which has a double-wall oil storage tube, and a mono tube-type shock absorber, which has a single wall oil storage tube.
The mono tube-type shock absorber employs a single tube, thereby providing merits of a very simple structure and easy assembly.
FIG. 1 shows one example of the mono tube type shock. The mono tube-type shock absorber 10 includes a single tube 11, a piston rod 12 inserted at one end thereof into the tube 11 and extending at the other end thereof through an upper end of the tube 11, a piston valve 13 provided to the one end of the piston rod 12 to divide the interior of the tube 11 into a rebound chamber 11 a at an upper side thereof and a compression chamber 11 b at a lower side thereof and having an oil passage formed therein for flow of a working oil between the rebound chamber 11 a and the compression chamber 11 b, a free piston 14 disposed inside the tube 11 to divide the tube 11 into the compression chamber 11 b above the free piston 14 and a gas chamber 11 c under the free piston 14, and a seal assembly 15 disposed on the upper end of the tube 11 to seal the upper end of the tube 11 while slidably supporting the piston rod 12.
The seal assembly 15 is composed of a rod guide and an oil seal. Further, the piston rod 12 is engaged at an upper end thereof with an upper fastener, such as an eye bolt 16 or other types of bolt, and with an upper cap 17 directly under the upper eye bolt 16 for installation of a dust cover (not shown).
Within the tube 11, the gas chamber 11c under the free piston 14 is filled with gas, and the rebound chamber 11a and the compression chamber 11b above the free piston 14 is filled with oil.
The tube 11 is generally formed at a lower end thereof with a gas injection hole through which the gas is supplied into the gas chamber 11c. Then, with the free piston 14 inserted into the tube 11, the gas is injected into the gas chamber 11c through the gas injection hole at the lower end of the tube 11. In this case, the upper end of the tube 11 is closed to prevent the free piston 14 from escaping through the upper end of the tube 11 when a lower space of the tube 11 is filled with the gas, and the gas injection hole is then welded to seal the gas chamber 11c. 
However, such a conventional gas encapsulating method involves welding of the gas injection hole, which causes generation of sludge during welding and requires cooling of the welded part after welding.
When supplying the oil into the rebound chamber 11a and the compression chamber 11b above the free piston 14, the piston rod 12 pushes down the free piston 14 to a desired position in the tube 11 to secure an oil storage space in the tube 11 with the gas chamber under the free piston 14 filled with the gas.
The length of the mono-tube-type shock absorber is determined according to the position of the free piston pushed down for supplying the oil. For example, when the piston rod 12 pushes down the free piston 14 to a deep position for supplying the oil as shown in (a) of FIG. 2, an overlapping area between the piston rod 12 and the tube 11 is relatively increased, thereby decreasing the length of the shock absorber. On the contrary, when the piston rod 12 pushes down the free piston 14 to a shallow position as shown in (b) of FIG. 2, an overlapping area between the piston rod 12 and the tube 11 is decreased, thereby increasing the length of the shock absorber.
Meanwhile, the seal assembly 15 fitted into the piston rod 12 is located outside at an upper side of the tube 11 while the oil is supplied into the tube 11, and is then inserted into the tube 11 after the tube 11 is filled with the oil. The seal assembly 15 is inserted into the tube 11 by a seal assembly inserting unit (not shown). Here, in order to descend and insert the seal assembly 15 into the tube 11, the seal assembly inserting unit must be brought into close contact with the piston rod 12 at an upper side of the tube 11.
However, when the piston rod 12 having the eye bolt 16 and the upper cap 17 coupled to the upper end thereof descends a relatively large distance as shown in (a) of FIG. 2, the distance between the upper end of the tube 11 and the upper cap 17 coupled to the upper end of the piston rod 12 decreases, so that a space for operation of the seal assembly inserting unit cannot be obtained.
Conventionally, as shown in (b) of FIG. 2, the piston rod 12 descends a relatively small distance to increase the distance between the upper end of the tube 11 and the upper cap 17 coupled to the upper end of the piston rod 12 in order to secure the space for operation of the seal assembly inserting unit. In this case, there is a problem in that the length of the shock absorber increases as described above.
On the contrary, in the case where the eye bolt 16 and the upper cap 17 are not coupled to the piston rod 12, the seal assembly inserting unit can be brought into close contact with the piston rod 12 even when the piston rod 12 descends a relatively large distance to the position shown in (a) of FIG. 2. In this case, after the oil is supplied to the tube 11 with the piston rod 12 deeply inserted to a position inside the tube 11, as shown in (a) of FIG. 2, the piston rod 12 is fitted into the seal assembly 15, thereby reducing the length of the shock absorber. In this case, however, since it is necessary to secure the piston rod 12 inside the tube 11 in order to couple the eye bolt 16 and the upper cap 17 to the upper end of the piston rod 12, which is not secured inside the tube 11, there is a need for a separate mechanism for securing the piston rod 12, thereby causing a complicated and time-consuming assembly operation.
To solve such problems in the art, the applicant developed an apparatus and method for encapsulating fluid in a shock absorber, as disclosed in Korean Patent No. 0880820. In this apparatus, a free piston is inserted into a tube after a gas is injected into the tube, and oil is injected into the tube after evacuating an upper space above the free piston to a vacuum though a hole formed at a upper side surface of the tube. Then, an oil seal-integrated rod guide is sealingly secured to an upper end of the tube by caulking.
Although the method and apparatus disclosed in Korean Patent No. 0880820 have various merits, for example, elimination of separate painting or tube surface treatment after assembly, the apparatus requires the use of only an oil seal-integrated rod guide and a rod guide separated from an oil seal cannot be used therefor. Moreover, only caulking can be employed to secure the rod guide in a final assembly stage of the shock absorber, and other methods such as curling cannot be used therefor.